Digitizer module, a waveform generating module, a converting method, a waveform generating method, and recording medium for recording a program thereof

ABSTRACT

A digitizer module comprises an AD converter for sampling a pair of analog signals at a predetermined time interval and converting into a first and second digital signals respectively, a second signal frequency component calculating unit for calculating a second signal frequency component representing a component of each frequency of the second digital signal on the basis of the second digital signal, a skew frequency component calculating unit for calculating a skew frequency component representing a phase error of each frequency of the second digital signal corresponding to the first digital signal on the basis of a skew of a timing with which the pair of analog signals are sampled by the AD converter and a second signal frequency component correcting unit for correcting the second signal frequency component on the basis of the skew frequency component.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a digitizer module, a waveformgenerating module, a converting method, a waveform generating method anda recording medium for recording a program thereof. More particularly,the present invention relates to a digitizer module for converting apair of analog signals into a pair of digital signals with equal sampletiming, a waveform generating module for outputting a pair ofsynchronous analog signals and a program and a method of processthereof.

[0003] 2. Description of the Related Art

[0004] As known in the art, with regard to a digitizer module forsampling a pair of analog signals such as quadrature modulated signalsto be synchronized each other, there has been a problem that if samplingtimings of a pair of AD converters sampling a pair of analog signals donot match each other, quality of observed signals is lowered due to animpairment of orthogonality regarding a result of measuring the twoanalog signals originally in quadrature.

[0005] And also, with regard to a waveform generating module forconverting a pair of digital signals to be synchronized each other intoanalog signals respectively and outputting the signals, if convertingtimings of a pair of DA converters converting a pair of digital signalsinto a pair of analog signals respectively do not match each other,quality of outputted signals is lowered due to a phase differencebetween a pair of analog signals, which are originally synchronized.

[0006] In order to prevent the impairment of quality of signal due tothe previous problems, an equal-length routing has been used withrespect to a clock signal of a pair of DA converters or a pair of ADconverters.

[0007] The difference of sample timing or converting timing previouslydescribed also results from differences between characteristics of ADconverters or DA converters and circuits or routing on other signaltrace. Consequently, in order to achieve a digitizer module or awaveform generating module with higher precision, it is desirable toprevent the impairment of quality of signal due to these causes, as wellas an equal-length routing with respect to a clock signal.

SUMMARY OF THE INVENTION

[0008] Therefore, it is an object of the present invention to provide adigitizer module, a waveform generating module, a converting method, awaveform generating method and a recording medium for recording aprogram thereof, which are capable of solving the problems above. Theabove and other objects can be achieved by combinations described in theindependent claims. The dependent claims define further advantageous andexemplary combinations of the present invention.

[0009] According to the first aspect of the present invention, adigitizer module for converting a pair of analog signals into a pair ofdigital signals with equal sample timing, comprises an AD converter forsampling the pair of analog signals at a predetermined time interval andconverting into a first and second digital signals respectively, asecond signal frequency component calculating unit for calculating asecond signal frequency component representing a component of eachfrequency of the second digital signal on the basis of the seconddigital signal, a skew frequency component calculating unit forcalculating a skew frequency component representing a phase error ofeach frequency of the second digital signal corresponding to the firstdigital signal on the basis of a skew of a timing with which the pair ofanalog signals are sampled by the AD converter and a second signalfrequency component correcting unit for correcting the second signalfrequency component on the basis of the skew frequency component.

[0010] A digitizer module may further comprise a corrected second signalcalculating unit for calculating the second digital signal on which theskew has been corrected on the basis of the second signal frequencycomponent, which is corrected.

[0011] The second signal frequency component calculating unit maycalculate the second signal frequency component by performing a discreteFourier-transform on the second digital signal, the skew frequencycomponent calculating unit may calculate a correcting function in afrequency domain for correcting the skew with the skew frequencycomponent and the second signal frequency component correcting unit maycorrect the second signal frequency component by multiplying the secondsignal frequency component by the correcting function in the frequencydomain.

[0012] A digitizer module may further comprise a first signal frequencycomponent calculating unit for calculating a first signal frequencycomponent representing a component of each frequency of the firstdigital signal on the basis of the first digital signal, wherein thesecond signal frequency component correcting unit may correct the secondsignal frequency component on the basis of the skew frequency componentand the first signal frequency component.

[0013] A digitizer module may further comprise a second signal frequencycomponent calculating unit for calculating a first signal frequencycomponent representing a component of each frequency of the firstdigital signal on the basis of the first digital signal and a firstsignal frequency component correcting unit for correcting the firstsignal frequency component on the basis of the skew frequency component.

[0014] A digitizer may further comprise a skew measuring unit formeasuring the skew on the basis of an amount of a phase differencebetween the first and second digital signals, in case a same signal asthe pair of analog signals is inputted to the AD converter.

[0015] According to the second aspect of the present invention, adigitizer module for converting a pair of analog signals into a pair ofdigital signals with equal sample timing, comprises an AD converter forsampling the pair of analog signals at a predetermined time interval andconverting into a first and a second digital signals, a first digitalfilter for generating a first converted signal into which the firstdigital signal is converted on the basis of a predetermined filtercoefficient, a correcting filter coefficient generator for generating acorrecting filter coefficient correcting a skew, besides a waveform ofan impulse response of the correcting filter coefficient is same as thefirst digital filter, on the basis of the skew of a timing with whichthe pair of analog signals are sampled by the AD converter and apredetermined filter coefficient and a second digital filter forconverting the second digital signal on the basis of the correctingfilter coefficient and generating a second converted signal on which theskew is corrected.

[0016] The correcting filter coefficient generator may make thecorrecting filter coefficient be h(k·T−τ), in case the predeterminedfilter coefficient is h(k·T) and the skew is τ, where the first digitalfilter has at least two the predetermined filter coefficient, k denotesan integer in a range of zero to a number one less than the number ofthe predetermined filter coefficient and T denotes a sampling intervalof the AD converter.

[0017] According to the third aspect of the present invention, awaveform generating module for outputting a pair of synchronous analogsignals, comprises a first digital signal calculating unit forgenerating a first digital signal on the basis of a first signalfrequency component representing a component of each frequency of afirst analog signal, which the waveform generating module should output,a second digital signal calculating unit for generating a second digitalsignal on the basis of a second signal frequency component representinga component of each frequency of a second analog signal, which thewaveform generating module should output, a DA converter for convertingthe first and second digital signals into the first and second analogsignals at a predetermined time interval respectively, a skew frequencycomponent calculating unit for calculating a skew frequency componentrepresenting a phase error of each frequency of the second analog signalcorresponding to the first analog signal, on the basis of a skew of atiming with which the first and second digital signals are converted bythe DA converter and a second signal frequency component correcting unitfor correcting the second signal frequency component used for generatingthe second digital signal by the second digital signal calculating uniton the basis of the skew frequency component.

[0018] The skew frequency component calculating unit may calculate acorrecting function in a frequency domain for correcting the skew withthe skew frequency component, the second signal frequency componentcorrecting unit may correct the second signal frequency component bymultiplying the second signal frequency component by the correctingfunction in the frequency domain and the second digital signalcalculating unit may generate the second digital signal by performing aninverse discrete Fourier-transform on the second signal frequencycomponent corrected by the second signal frequency component correctingunit.

[0019] The second signal frequency component correcting unit may correctthe second signal frequency component used for generating the seconddigital signal by the second digital signals calculating unit, on thebasis of the skew frequency component and the first signal frequencycomponent.

[0020] A waveform generating module may further comprise a first signalfrequency component correcting unit for correcting the first signalfrequency component used for generating the first digital signal by thefirst digital signal calculating unit, on the basis of the skewfrequency component.

[0021] A waveform generating module may further comprise a skewmeasuring unit for measuring the skew on the basis of an amount of aphase difference between the first and second analog signals, in case asame signal as the first and second digital signals is inputted to theDA converter.

[0022] According to the fourth aspect of the present invention, awaveform generating module for outputting a pair of synchronous analogsignals, comprises a first digital filter for generating a firstconverted signal into which a first digital signal, which represents asignal value of a first analog signal to be outputted, is converted onthe basis of a first filter coefficient, a second digital filter forgenerating a second converted signal into which a second digital signal,which represents a signal value of a second analog signal to beoutputted, is converted on the basis of a second filter coefficient, aDA converter for converting the first and second digital signals intothe first and second analog signals at a predetermined time intervalrespectively and a correcting filter coefficient generator forgenerating the second filter coefficient correcting a skew, besides awaveform of an impulse response of the correcting filter coefficient issame as the first digital filter, on the basis of the skew of a timingwith which the DA converter converts the first and second digitalsignals into the first and second analog signals and the first filtercoefficient.

[0023] The correcting filter coefficient generator may make the secondfilter coefficient be h(k·T−τ), in case the first filter coefficient ish(k·T) and the converting timing error is τ, where the first digitalfilter has at least two the first filter coefficient, k denotes aninteger in a range of zero to a number one less than the number of thefirst filter coefficient and T denotes a converting interval of the DAconverter.

[0024] According to the fifth aspect of the present invention, arecording medium for recording a program used for a digitizer moduleconverting a pair of analog signals into a pair of digital signals withequal sample timing is provided, wherein the digitizer module comprisesan AD converter for sampling the pair of analog signals at apredetermined time interval and converting the pair of analog signalsinto a first and second digital signals, and the program allows thedigitizer module to function with a second signal frequency componentcalculating unit for calculating a second signal frequency componentrepresenting a component of each frequency of the second digital signalon the basis of the second digital signal, a skew frequency componentcalculating unit for calculating a skew frequency component representinga phase error of each frequency of the second digital signalcorresponding to the first digital signal, on the basis of the skew of atiming with which the pair of analog signals are sampled by the ADconverter and a second signal frequency component correcting unit forcorrecting the second signal frequency component on the basis of theskew frequency component.

[0025] According to the sixth aspect of the present invention, aconverting method for converting a pair of analog signals into a pair ofdigital signals with equal sample timing, comprises the steps ofsampling the pair of analog signals at a predetermined time interval andconverting the pair of analog signals into a first and second digitalsignals respectively, calculating a second signal frequency componentrepresenting a component of each frequency of the second digital signalon the basis of the second digital signal, calculating a skew frequencycomponent representing a phase error of each frequency of the seconddigital signal corresponding to the first digital signal, on the basisof the skew of a timing with which the pair of analog signals aresampled during the step of sampling and converting and correcting thesecond signal frequency component on the basis of the skew frequencycomponent.

[0026] According to the seventh aspect of the present invention, arecording medium for recording a program used for a digitizer moduleconverting a pair of analog signals into a pair of digital signals withequal sample timing is provided, wherein the digitizer module comprisesan AD converter for sampling the pair of analog signals at apredetermined time interval and converting the pair of analog signalsinto a first and second digital signals, and the program allows thedigitizer module to function with a first digital filter for generatinga first converted signal into which the first digital signal isconverted on the basis of a predetermined filter coefficient acorrecting filter coefficient generator for generating a correctingfilter coefficient correcting a skew, besides a waveform of an impulseresponse of the correcting filter coefficient is same as the firstdigital filter, on the basis of the skew of a timing with which thefirst and second analog signals are converted by the AD converter andthe predetermined filter coefficient and a second digital filter forconverting the second digital signal on the basis of the correctingfilter coefficient and generating a second converted signal on which theskew is corrected.

[0027] According to the eighth aspect of the present invention, aconverting method for converting a pair of analog signals into a pair ofdigital signals with equal sample timing, comprises the steps ofsampling the pair of analog signals at a predetermined time interval andconverting the pair of analog signals into a first and second digitalsignals respectively, generating a first converted signal into which thefirst digital signal is converted on the basis of a predetermined filtercoefficient, generating a correcting filter coefficient correcting askew, besides a waveform of an impulse response of the correcting filtercoefficient is same as the step of generating the first convertedsignal, on the basis of the skew of a timing with which the first andsecond analog signals are converted by the AD converter and thepredetermined filter coefficient and converting the second digitalsignal on the basis of the correcting filter coefficient and generatinga second converted signal on which the skew is corrected.

[0028] According to the ninth aspect of the present invention, arecording medium for recording a program used for a waveform generatingmodule outputting a pair of synchronous analog signals is provided,wherein the waveform generating module comprises a DA converter forconverting a first and second digital signals into a first and secondanalog signals at a predetermined time interval respectively, and theprogram allows the waveform generating module to function with a firstdigital signal calculating unit for generating the first digital signalon the basis of a first signal frequency component representing acomponent of each frequency of the first analog signal, which should beoutputted by the waveform generating module a second digital signalcalculating unit for generating the second digital signal on the basisof a second signal frequency component representing a component of eachfrequency of the second analog signal, which should be outputted by thewaveform generating module a skew frequency component calculating unitfor calculating a skew frequency component representing a phase error ofeach frequency of the second analog signal corresponding to the firstanalog signal, on the basis of the skew of a timing with which the firstand second digital signals are converted by the DA converter and asecond signal frequency component correcting unit for correcting thesecond signal frequency component used for generating the second digitalsignal by the second digital signal calculating unit, on the basis ofthe skew frequency component.

[0029] According to the tenth aspect of the present invention, awaveform generating method for outputting a pair of synchronous analogsignals, comprises the steps of generating a first digital signal on thebasis of a first signal frequency component representing a component ofeach frequency of a first analog signal, which should be outputted,generating a second digital signal on the basis of a second signalfrequency component representing a component of each frequency of asecond analog signal, which should be outputted, converting the firstand second digital signals into the first and second analog signals at apredetermined time interval respectively, calculating a skew frequencycomponent representing a phase error of each frequency of the secondanalog signal corresponding to the first analog signal, on the basis ofa skew of a timing with which the first and second digital signals areconverted during the step of converting and correcting the second signalfrequency component used for generating the second digital signal duringthe step of generating the second digital signal, on the basis of theskew frequency component.

[0030] According to the eleventh aspect of the present invention, arecording medium for recording a program used for a waveform generatingmodule outputting a pair of synchronous analog signals is provided,wherein the waveform generating module comprises a DA converter forconverting a first and second digital signals into a first and secondanalog signals at a predetermined time interval respectively, and theprogram allows the waveform generating module to function with a firstdigital filter for generating a first converted signal into which afirst digital signal, which represents a signal value of the firstanalog signal to be outputted, is converted on the basis of a firstfilter coefficient, a second digital filter for generating a secondconverted signal into which a second digital signal, which represents asignal value of the second analog signal to be outputted, is convertedon the basis of a second filter coefficient and a correcting filtercoefficient generator for generating the second filter coefficientcorrecting a skew, besides a waveform of an impulse response of thecorrecting filter coefficient is same as the first digital filter, onthe basis of the skew of a timing with which the first and seconddigital signals converted into the first and second analog signals bythe DA converter and the first filter coefficient.

[0031] According to the twelfth aspect of the present invention, awaveform generating method for outputting a pair of synchronous analogsignals, comprises the steps of generating a first converted signal intowhich a first digital signal, which represents a signal value of a firstanalog signal to be outputted, is converted on the basis of a firstfilter coefficient, generating a second converted signal into which asecond digital signal, which represents a signal value of a secondanalog signal to be outputted, is converted on the basis of a secondfilter coefficient, converting the first and second digital signals intothe first and second analog signals at a predetermined time intervalrespectively and generating the second filter coefficient correcting askew, besides a waveform of an impulse response of the second filtercoefficient is same as the first digital filter, on the basis of theskew of a timing with which the first and second digital signalsconverted into the first and second analog signals during the step ofconverting and the first filter coefficient.

[0032] The summary of the invention does not necessarily describe allnecessary features of the present invention. The present invention mayalso be a sub-combination of the features described above. The above andother features and advantages of the present invention will become moreapparent from the following description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0033]FIG. 1 shows a configuration of a digitizer apparatus 100 relatingto the first exemplary embodiment of the present invention.

[0034]FIG. 2 shows a process flow of a digitizer apparatus 100 relatingto the first exemplary embodiment of the present invention.

[0035]FIG. 3 shows a configuration of a waveform generating apparatus300 relating to the second exemplary embodiment of the presentinvention.

[0036]FIG. 4 shows a process flow of a waveform generating apparatus 300relating to the second exemplary embodiment of the present invention.

[0037]FIG. 5 shows a configuration of a digitizer apparatus 500 relatingto the third exemplary embodiment of the present invention.

[0038]FIG. 6 shows a process flow of a digitizer apparatus 500 relatingto the third exemplary embodiment of the present invention.

[0039]FIG. 7 shows a configuration of a waveform generating apparatus700 relating to the fourth exemplary embodiment of the presentinvention.

[0040]FIG. 8 shows a process flow of a waveform generating apparatus 700relating to the fourth exemplary embodiment of the present invention.

[0041]FIG. 9 shows an exemplary hardware configuration of a digitizerapparatus 100, a waveform generating apparatus 300, a digitizerapparatus 500 and/or a waveform generating apparatus 700 relating to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0042] The invention will now be described based on the preferredembodiments, which do not intend to limit the scope of the presentinvention, but exemplify the invention. All of the features and thecombinations thereof described in the embodiments are not necessarilyessential to the invention.

[0043]FIG. 1 shows a configuration of a digitizer apparatus 100 relatingto the first exemplary embodiment of the present invention. Thedigitizer apparatus 100 converts a pair of analog signals to be observedin synchronized state into a pair of digital signals with equal sampletiming. The digitizer apparatus 100, with regard to this conversion,corrects an error from sample timing with which a pair of analog signalsis converted into digital signals by a digital process so that animpairment of quality of signal can be prevented during digitizing apair of analog signals. The digitizer apparatus 100 includes an analoginput unit 101, an AD converter 110 and a correcting process unit 120.

[0044] The analog input unit 101 inputs an analog I input signal and ananalog Q input signal in quadrature each other, an example of a pair ofanalog signals to be observed in the synchronized state. The analoginput unit 101 includes a reference signal generator 102 a multiplexer104, a multiplexer 105, a first analog unit 106 and a second analog unit108.

[0045] The reference signal generator 102 generates a reference signal,which the correcting process unit 120 uses to measures a skew, an errorof timing with which a pair of analog signals are sampled by the ADconverter 110. The multiplexer 104 and the multiplexer 105 input thesame reference signal to the AD converter 110 via the first analog unit106 or the second analog unit 108, in case the digitizer apparatus 100measures the skew. And, in case that the digitizer apparatus 100 samplesthe analog I input signal and the analog Q input signal, The multiplexer104 and the multiplexer 105 input these signals to the AD converter 110via the first analog unit 106 or the second analog unit 108. The firstanalog unit 106 and the second analog unit 108 are an analog circuit,which input the analog I input signal and the analog Q input signal fromthe multiplexer 104 or the multiplexer 105, for example conduct aconversion of signal level and input the signals to the AD converter110.

[0046] The AD converter 110 samples a pair of analog signals inputtedvia the analog input unit 101 with a sampling interval, a predeterminedtime interval, and converts the signals into a first digital signal anda second digital signal. The AD converter 110 includes a reference clockgenerator 112, a first AD converter 114 and a second AD converter 116.

[0047] The reference clock generator 112 generates a sampling clocksignal representing sampling timing with which the first AD converter114 and the second AD converter 116 sample a pair of analog signalsinputted from the analog input unit 101. The first AD converter 114converts the analog I input signal into a digital I signal, an exampleof the first digital signal on the basis of the sampling clock signal.The second AD converter 116 converts the analog Q input signal into adigital Q signal, an example of the second digital signal on the basisof the sampling clock signal.

[0048] The correcting process unit 120 corrects an error of sampletiming with respect to a pair of digital signals and outputs a pair ofdigital signals with equal sample timing. The correcting process unit120 includes a first signal frequency component calculating unit 122, asecond signal frequency component calculating unit 124, a skew frequencycomponent calculating unit 126, a first signal frequency correcting unit128, a second signal frequency correcting unit 130, a skew measuringunit 132, a corrected first signal calculating unit 140 and a correctedsecond signal calculating unit 142.

[0049] The first signal frequency component calculating unit 122calculates I signal frequency components, an example of first signalfrequency components representing components of each frequency of thedigital I signal, on the basis of the digital I signal. The secondsignal frequency component calculating unit 124 calculates Q signalfrequency components, an example of second signal frequency componentsrepresenting components of each frequency of the digital Q signal, onthe basis of the digital Q signal. More particularly, the first signalfrequency component calculating unit 122 and the second signal frequencycomponent calculating unit 124 may calculate the I signal frequencycomponents or the Q signal frequency components, the digital I signal orthe digital Q signal in frequency domain, by performing discreteFourier-transform of the digital I signal or the digital Q signal oftime domain respectively.

[0050] The skew frequency component calculating unit 126 calculates skewfrequency components representing phase errors of each frequency of thedigital Q signal with respect to the digital I signal, on the basis of askew of sampling timing with which a pair of analog signals is sampledby the AD converter 110. More particularly, the skew frequency componentcalculating unit 126 may calculate a correcting function in thefrequency domain correcting the skew with the frequency components.

[0051] The second signal frequency correcting unit 130 convertscomponents at each frequency with the same sample timing as the I signalfrequency components, by correcting the Q signal frequency components onthe basis of the skew frequency components calculated by the skewfrequency component calculating unit 126. More particularly, the asecond signal frequency correcting unit 130 may correct the Q signalfrequency components by multiplying the Q signal frequency components bythe correcting function in the frequency domain calculated by the skewfrequency component calculating unit 126. And, the second signalfrequency correcting unit 130 may correct the Q signal frequencycomponents on the basis of the skew frequency components and the Isignal frequency components.

[0052] The first signal frequency correcting unit 128 convertscomponents at each frequency with the same sample timing as the Q signalfrequency components, by correcting the I signal frequency components onthe basis of the skew frequency components calculated by the skewfrequency component calculating unit 126. More particularly, the a firstsignal frequency correcting unit 128 may correct the I signal frequencycomponents by multiplying the I signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 126. And, the first signalfrequency correcting unit 130 may correct the I signal frequencycomponents on the basis of the skew frequency components and the Qsignal frequency components. Here, in case that the second signalfrequency correcting unit 130 completely corrects the skew componentswith respect to the Q signal frequency components, the first signalfrequency correcting unit 128 may, without changing the I signalfrequency components, output to the corrected first signal calculatingunit 140.

[0053] The skew measuring unit 132 measures the skew of sampling timingwith which a pair of analog signals inputted to the digitizer apparatus100 is sampled by the AD converter 110, and provides the skew to theskew frequency component calculating unit 126. The skew measuring unit132 relating to the exemplary embodiment of the present inventionmeasures the skew on the basis of an amount of a phase differencebetween the digital I signal and the digital Q signal outputted from thefirst AD converter 114 and the second AD converter 116, in case the samereference signal generated by the reference signal generator 102 withrespect to a pair of analog signals is inputted to the AD converter 110.

[0054] The corrected first signal calculating unit 140 calculates andoutputs corrected digital I signal on which the skew is corrected on thebasis of the I signal frequency components corrected by the first signalfrequency correcting unit 128. More particularly, the corrected firstsignal calculating unit 140 converts the I signal frequency components,spectrums of the digital I signal in the frequency domain, corrected bythe first signal frequency correcting unit 128, into the correcteddigital I signal in the time domain by, for example, performing theinverse discrete Fourier-transform. The corrected second signalcalculating unit 142, like the corrected first signal calculating unit140, calculates and outputs corrected digital Q signal on which the skewis corrected on the basis of the Q signal frequency components correctedby the second signal frequency correcting unit 130.

[0055] Next, an exemplary method for correcting the skew will bedescribed with regard to the digitizer apparatus 100.

[0056] Letting i(t) and q(t) be the analog I signal and the analog Qsignal in the time domain respectively, which is inputted to thedigitizer apparatus 100, pi(t) and pq(t) be each sampling clock signalof the analog I signal and the analog Q signal, T be an samplinginterval of the first AD converter 114 and the second AD converter 116and τ be the skew of the first AD converter 114 and the second ADconverter 116, pi(t) and pq(t) can be represented as the followingequations(1) and (2) respectively: $\begin{matrix}{{p_{i}(t)} = {\sum\limits_{k = {- \infty}}^{\infty}\quad {\delta \left( {t - {kT}} \right)}}} & (1) \\{{p_{q}(t)} = {\sum\limits_{k = {- \infty}}^{\infty}\quad {{\delta \left( {t - {kT} - \tau} \right)}.}}} & (2)\end{matrix}$

[0057] If i(t) and q(t) is sampled using pi(t) and pq(t) with regard tothe first AD converter 114 and the second AD converter 116, iskew(t) andqskew(t), a sampled digital I signal and a sampled digital Q signalincluding skew components, are the following equations(3) and (4)respectively: $\begin{matrix}{{i_{skew}(t)} = {{i(t)}{\sum\limits_{k = {- \infty}}^{\infty}\quad {\delta \left( {t - {kT}} \right)}}}} & (3) \\{{q_{skew}(t)} = {{q(t)}{\sum\limits_{k = {- \infty}}^{\infty}\quad {{\delta \left( {t - {kT} - \tau} \right)}.}}}} & (4)\end{matrix}$

[0058] If the Fourier-transform is performed of iskew(t) and qskew(t)with regard to the first signal frequency component calculating unit 122and the second signal frequency component calculating unit 124, the Isignal frequency components Iskew(f) and the Q signal frequencycomponents Qskew(f) are the following equations(5) and (6) respectively:$\begin{matrix}{{I_{skew}(f)} = {{{I(f)}*\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}\quad {\delta \left( {f - \frac{k}{T}} \right)}}} = {\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}\quad {I\left( {f - \frac{k}{T}} \right)}}}}} & (5) \\{{Q_{skew}(f)} = {{{Q(f)}*^{{- 2}\quad \pi \quad f\quad \tau}\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}\quad {\delta \left( {f - \frac{k}{T}} \right)}}} = {\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}\quad {{Q\left( {f - \frac{k}{T}} \right)}{^{{- {j2}}\quad \pi \quad k\quad {\tau/T}}.}}}}}} & (6)\end{matrix}$

[0059] Here, letting x(t)=i(t)+j·q(t), a complex signal in the timedomain inputted to the digitizer apparatus 100, and X(f)=I(f)+j·Q(f),the Fourier-transform of x(t), Xskew(f), a complex signal in thefrequency domain outputted by the first signal frequency componentcalculating unit 122 and the second signal frequency componentcalculating unit 124, is the following equation(7): $\begin{matrix}{{X_{skew}(f)} = {{{I_{skew}(f)} + {j\quad {Q_{skew}(f)}}} = {{\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}\quad {I\left( {f - \frac{k}{T}} \right)}}} + {j\frac{1}{T}{\sum\limits_{k = {- \infty}}^{\infty}{{Q\left( {f - \frac{k}{T}} \right)}{^{{- j}\quad 2\pi \quad k\quad {\tau/T}}.}}}}}}} & (7)\end{matrix}$

[0060] Here, using X(f) and X*(f), the conjugate function of X(f), I(f)and Q(f) are represented as the following equations(8) and (9)respectively: $\begin{matrix}{{I(f)} = {\frac{1}{2}\left\{ {{X(f)} + {X^{*}\left( {- f} \right)}} \right\}}} & (8) \\{{j\quad {Q(f)}} = {\frac{1}{2}{\left\{ {{X(f)} - {X^{*}\left( {- f} \right)}} \right\}.}}} & (9)\end{matrix}$

[0061] From equations(7) and (9), the following equation(10) is derived:$\begin{matrix}\begin{matrix}{{X_{skew}(f)} = {\frac{1}{2T}{\sum\limits_{k = {- \infty}}^{\infty}\quad \left\lbrack {{X\left( {f - \frac{k}{T}} \right)} + {X^{*}\left( {{- f} + \frac{k}{T}} \right)} + \left( {{X\left( {f - \frac{k}{T}} \right)} -} \right.} \right.}}} \\\left. {\left. {X^{*}\left( {{- f} + \frac{k}{T}} \right)} \right)^{{- {j2}}\quad \pi \quad k\quad {\tau/T}}} \right\rbrack \\{= {\frac{1}{2T}{\sum\limits_{k = {- \infty}}^{\infty}\quad \left\lbrack {{{X\left( {f - \frac{k}{T}} \right)}\left( {1 + ^{{- j}\quad 2\pi \quad k\quad {\tau/T}}} \right)} + {X^{*}\left( {{- f} + \frac{k}{T}} \right)}} \right.}}} \\{\left. \left( {1 - ^{{- {j2}}\quad \pi \quad k\quad {\tau/T}}} \right) \right\rbrack.}\end{matrix} & (10)\end{matrix}$

[0062] For example, considering the discrete Fourier-transform for k=0or k=1 with regard to the first signal frequency component calculatingunit 122 and the second signal frequency component calculating unit 124,Iskew(f) and Qskew(f), on the basis of equations(5), (6), (8) and (9),are the following equations(11) and (12) respectively: $\begin{matrix}{{I_{skew}(f)} = {\frac{1}{2T}\left\{ {{X(f)} + {X^{*}\left( {- f} \right)} + {X\left( {f - \frac{1}{T}} \right)} + {X^{*}\left( {{- f} + \frac{1}{T}} \right)}} \right\}}} & (11) \\{{{jQ}_{skew}(f)} = {\frac{1}{2T}{\left\{ {{X(f)} - {X^{*}\left( {- f} \right)} + {\left( {{X\left( {f - \frac{1}{T}} \right)} - {X^{*}\left( {{- f} + \frac{1}{T}} \right)}} \right)^{{- j}\quad 2\pi \quad {\tau/T}}}} \right\}.}}} & (12)\end{matrix}$

[0063] In order to eliminate a term X*(−f+1/T) for k=1 fromequations(11) and (12), it is corrected that Qskew(f) is multiplied byej2πτ/T. Here, Xc(f), a corrected complex signal in the frequencydomain, using equation(10) for k=0 or k=1, can be represented as thefollowing equation(13): $\begin{matrix}\begin{matrix}{{X_{c}(f)} = {{I_{skew}(f)} + {j\quad ^{j\quad 2\pi \quad {\tau/T}}{Q_{skew}(f)}}}} \\{= {\frac{1}{2}\left\lbrack {{X_{skew}(f)} + {X_{skew}^{*}\left( {- f} \right)} + {\left\{ {{X_{skew}(f)} - {X_{skew}^{*}\left( {- f} \right)}} \right\} ^{j\quad 2\pi \quad {\tau/T}}}} \right\rbrack}} \\{= {\frac{1}{2}\left\lbrack {{{X_{skew}(f)}\left( {1 + ^{j\quad 2\pi \quad {\tau/T}}} \right)} + {{X_{skew}^{*}\left( {- f} \right)}\left( {1 - ^{j\quad 2\pi \quad {\tau/T}}} \right)}} \right\rbrack}} \\{= {{^{j\quad 2\pi \quad {\tau/T}}\left\lbrack {{{X_{skew}(f)}{\cos \left( {\pi \quad {\tau/T}} \right)}} - {j\quad {X_{skew}^{*}(f)}{\sin \left( {\pi \quad {\tau/T}} \right)}}} \right\rbrack}.}}\end{matrix} & (13)\end{matrix}$

[0064] Here, performing the inverse Fourier-transform of [ ] part inequation(13), the following equation(10) is derived: $\begin{matrix}{{{Inv}\quad {Fourier}\left\{ \left\lbrack {{{X_{skew}(f)}{\cos \left( {\pi \quad {\tau/T}} \right)}} - {j\quad {X_{skew}^{*}\left( {- f} \right)}{\sin \left( {\pi \quad {\tau/T}} \right)}}} \right\rbrack \right\}}\quad = {{{{\cos \left( {\pi \quad {\tau/T}} \right)}{x_{skew}(t)}} - {j\quad {\sin \left( {\pi \quad {\tau/T}} \right)}{x_{skew}^{*}(t)}}}\quad = {{{{\cos \left( {\pi \quad {\tau/T}} \right)}\left\{ {{i_{skew}(t)} + {j\quad {q_{skew}(t)}}} \right\}} - {{{jsin}\left( {\pi \quad {\tau/T}} \right)}\left\{ {{i_{skew}(t)} - {j\quad {q_{skew}(t)}}} \right\}}}\quad = {{\left\{ {{{i_{skew}(t)}{\cos \left( {\pi \quad {\tau/T}} \right)}} - {{q_{skew}(t)}{\sin \left( {\pi \quad {\tau/T}} \right)}}} \right\} \quad + \left\{ {{{q_{skew}(t)}{\cos \left( {\pi \quad {\tau/T}} \right)}} - {{i_{skew}(t)}{\sin \left( {\pi \quad {\tau/T}} \right)}}} \right\}}\quad = {{i^{\prime}(t)} + {j\quad {{q^{\prime}(t)}.}}}}}}} & (14)\end{matrix}$

[0065] I′(t) and q′(t) in equation(10) represent signals, which deviatefrom a rectangular coordinate of the digital I signal and the digital Qsignal and are in angular rotation on the basis of τ. That is to say,the digital I signal and the digital Q signal are analyzed withconverting to I′ axis and Q′ axis in a coordinate system in which thedigital I signal and the digital Q signal are in angular rotation on thebasis of τ. In order to adjust I′ axis in regard to equation(14) to Iaxis, Xc(f) is changed to the following equation(15):

X _(c)(f)=e ^(−j2πτ/T) [I _(skew) (f)+je ^(2πτ/T) Q _(skew) (f)]  (15).

[0066] Equation(15) is applied to the discrete Fourier-transform. Here,the discrete Fourier-transform of xskew(t) is the followingequation(16): $\begin{matrix}\begin{matrix}{{\left\lbrack {\int_{- \infty}^{\infty}{{X_{skew}(t)}^{{- 2}\quad \pi \quad f\quad t}\quad {t}}} \right\rbrack_{f = {k/{NT}}} = {\int_{- \infty}^{\infty}\left\{ {{{i_{skew}(t)}{p_{i}(t)}} + {{q_{skew}(t)}{p_{q}(t)}}} \right\}}}\quad} \\{{^{{- {j2\pi}}\quad f\quad t}{t}}} \\{= {{\sum\limits_{m = 0}^{N - 1}\quad {{i_{skew}({mT})}^{{- j}\quad 2\pi \quad k\quad {m/N}}}} + ^{{- j}\quad 2\pi \quad {{kt}/{NT}}}}} \\{{\sum\limits_{m = 0}^{N - 1}\quad {{q_{skew}({mT})}^{{- j}\quad 2\pi \quad k\quad {m/N}}}}} \\{= {{{DFT}_{I}(k)} + {^{{- j}\quad 2\pi \quad {{kt}/{NT}}}{{{DFT}_{Q}(k)}.}}}}\end{matrix} & (16)\end{matrix}$

[0067] From equations(15) and (16), the following equation(17) isderived: $\begin{matrix}\begin{matrix}{{X\left( \frac{k}{NT} \right)} = {^{{- j}\quad \pi \quad {\tau/T}}\left\lbrack {{{DFT}_{I}(k)} + {^{j\quad 2\pi \quad {\tau/T}}^{{- {j2}}\quad \pi \quad k\quad {\tau/{NT}}}{{DFT}_{Q}(k)}}} \right\rbrack}} \\{= {{^{{- j}\quad \pi \quad {\tau/T}}\left\lbrack {{{DFT}_{I}(k)} + {^{{j2\pi}\quad {{\tau {({1 - {k/N}})}}/T}}{{DFT}_{Q}(k)}}} \right\rbrack}.}}\end{matrix} & (17)\end{matrix}$

[0068] That is, in case equation (17) is provided, the first signalfrequency component calculating unit 122 and the second signal frequencycomponent calculating unit 124 perform the discrete Fourier-transform ofthe digital I signal and the digital Q signal outputted by the first ADconverter 114 and the second AD converter 116 and calculate DFTI(k) andDFTQ(k), the I signal frequency components and the Q signal frequencycomponents, respectively. The skew frequency component calculating unit126 calculates a pair of skew frequency components of e−jπτ/T andej2πτ(1−k/N)/T on the basis of the skew τ. The first signal frequencycorrecting unit 128 and the second signal frequency correcting unit 130calculate corrected I signal frequency components and corrected Q signalfrequency components on the basis of the skew frequency components.Therefore, The first signal frequency correcting unit 128 and the secondsignal frequency correcting unit 130 can calculate equation(17).

[0069] And, in case the analog I input signal and the analog Q inputsignal are such as base band signals, a band, the digitizer apparatus100 should manage, is within ±nyquist frequency. Here, in case the bandis limited within the nyquist frequencies, equations corresponding to anegative input signal frequency, which multiply components for k=1, thatis, spectrums between the nyquist frequency and a sampling frequency bycorrecting coefficiency ej2πτ/T l resulting from equation (13) ismultiplied by j·Qskew(f), are the following equations(18-1) and (18-2):

[0070] 0≦k<N/2(0˜nyquist frequency) $\begin{matrix}{{X\left( \frac{k}{NT} \right)} = {{{DFT}_{I}(k)} + {^{{- j}\quad 2\pi \quad {{k\tau}/{NT}}}{{DFT}_{Q}(k)}}}} & \left( {18\text{-}1} \right)\end{matrix}$

[0071] N/2≦k<N (nyquist frequency ˜sampling frequency) $\begin{matrix}\begin{matrix}{{X\left( \frac{k}{NT} \right)} = {{{DFT}_{I}(k)} + {^{j\quad 2\pi \quad {\tau/T}}^{{- {j2\pi}}\quad {{k\tau}/{NT}}}{{DFT}_{Q}(k)}}}} \\{= {{{DFT}_{I}(k)} + {^{j\quad 2\pi \quad {{\tau {({1 - {k/N}})}}/T}}{{{DFT}_{Q}(k)}.}}}}\end{matrix} & \left( {18\text{-}2} \right)\end{matrix}$

[0072] Moreover, in this regards, the correcting process unit 120 mayuse the I signal frequency components and the Q signal frequencycomponents outputted by the first signal frequency correcting unit 128and the second signal frequency correcting unit 130 as a pair of digitalsignals with equal sample timing without the corrected first signalcalculating unit 140 and the corrected second signal calculating unit142. And, instead of measuring the skew on the basis of the amount of aphase difference between the digital I signal and the digital Q signaloutputted by the first AD converter 114 and the second AD converter 116,the skew measuring unit 132 may, in case the reference signal generator102 inputs the same reference signal to the AD converter 110, adjust anamount of the correction for an optimum skew by measuring the skew ofthe digital I signal and the digital Q signal outputted by the correctedfirst signal calculating unit 140 and the corrected second signalcalculating unit 142 after the correction, changing the amount of thecorrection for the skew set by the skew frequency component calculatingunit 126.

[0073]FIG. 2 shows a process flow of a digitizer apparatus 100 relatingto the first exemplary embodiment of the present invention. First, inorder to measure the skew of sample timing of the first AD converter 114and the second AD converter 116, the reference signal generator 102inputs the reference signal to the first AD converter 114 via themultiplexer 104 and the first analog unit 106, while inputting the samereference signal to the second AD converter 116 via the multiplexer 105and the second analog unit 108(S200). The first AD converter 114 and thesecond AD converter 116 convert the reference signal inputted into thedigital I signal and the digital Q signal respectively(S210). The skewmeasuring unit 132 measures the skew on the basis of the amount of thephase difference between the digital I signal and the digital Qsignal(S220) And, the skew frequency component calculating unit 126calculates the skew frequency components representing the phase errorsof each frequency of the digital Q signal corresponding to the digital Isignal on the basis of the skew measured by the skew measuring unit132(S230).

[0074] Next, the AD converter 110 inputs the analog I signals via themultiplexer 104 and the first analog unit 106, while inputting theanalog Q signal via the multiplexer 105 and the second analog unit 108(S240). And, the first AD converter 114 and the second AD converter 116in the AD converter 110 sample the pair of analog signals inputted, andconvert to the digital I signal and digital Q signal respectively(S250).

[0075] Next, the first signal frequency component calculating unit 122calculates the I signal frequency components on the basis of the digitalI signal, and the second signal frequency component calculating unit 124calculates the Q signal frequency components on the basis of the digitalQ signal(S260). And, the first signal frequency correcting unit 128 andthe second signal frequency correcting unit 130 correct the I signalfrequency components and the Q signal frequency components on the basisof the skew frequency components calculated by the skew frequencycomponent calculating unit 126(S270). And, the corrected first signalcalculating unit 140 and the corrected second signal calculating unit142 calculate the corrected digital I signal and the corrected digital Qsignal on which the skew is corrected, on the basis of the corrected Isignal frequency components and the corrected Q signal frequencycomponents(S280).

[0076] According to the digitizer apparatus 100 described above, theskew of the sampling timing with which a pair of analog signals aresampled by the AD converter 110 can be corrected for a frequency band ofthe digital signal sampled by the AD converter 110. In addition, amagnitude of the skew during operation is measured by the referencesignal generator 102 and the skew measuring unit 132 and the amount ofthe correction can be adjusted using the magnitude of the skew measuredso that the digitizer apparatus 100 with high precision can be achieved.

[0077]FIG. 3 shows a configuration of a waveform generating apparatus300 relating to the second exemplary embodiment of the presentinvention. The waveform generating apparatus 300 inputs a pair ofdigital input signals to be converted into analog signals synchronized,and converts to and outputs a pair of analog signals synchronized. Withregard to the conversion, the waveform generating apparatus 300 preventsan impairment of quality of signal during converting a pair of digitalinput signals to analog signals by correcting an error of convertingtiming with which a pair of digital input signals are converted intoanalog signals respectively, with a digital process. The waveformgenerating apparatus 300 includes a correcting process unit 320 and a DAconverter 380.

[0078] The correcting process unit 320 inputs digital I input signal anddigital Q input signal in quadrature each other, an example of a pair ofdigital input signals to be converted to analog signals synchronized.The correcting process unit 320 includes a reference signal generator322, a skew measuring unit 323, a first signal frequency componentcalculating unit 324, a second signal frequency component calculatingunit 325, skew frequency component calculating unit 326, a first signalfrequency component correcting unit 328, a second signal frequencycomponent correcting unit 330, a first digital signal calculating unit332, a second digital signal calculating unit 334, a multiplexer 338 anda multiplexer 340.

[0079] The reference signal generator 322 generates a reference signal,which the skew measuring unit 323 uses to measure a skew, an error oftiming with which a pair of digital input signals are converted by theDA converter 380. The skew measuring unit 323 measures the skew of thetiming with which a pair of digital signals outputted by the correctingprocess unit 320 to DA converter 380 are converted by the DA converter380, and provides the skew to the first signal frequency componentcalculating unit 324. The skew measuring unit 323, according to thisexemplary embodiment, inputs the same reference signal generated by thereference signal generator 322 with a pair of digital signals to the DAconverter 380 via the multiplexer 338 and the multiplexer 340. And, inthis case, the skew measuring unit 323 measures the skew on the basis ofan amount of a phase difference between an analog I signal and an analogQ signal, an example of a first analog signal and a second analog signaloutputted by a first DA converter 384 and a second DA converter 386 inthe DA converter 380.

[0080] The first signal frequency component calculating unit 324, aconfiguration of which is the same as the first signal frequencycomponent calculating unit 122 regarding FIG. 1, calculates I signalfrequency components on the basis of the digital I input signal, anoriginal data of the analog I signal to be outputted by the waveformgenerating apparatus 300. Here, the I signal frequency components are anexample of first signal frequency components and represent components ofeach frequency of the analog I signal to be outputted by the waveformgenerating apparatus 300. The second signal frequency componentcalculating unit 325, a configuration of which is the same as the secondsignal frequency component calculating unit 124 regarding FIG. 1,calculates Q signal frequency components on the basis of the digital Qinput signal, an original data of the analog Q signal to be outputted.Here, the Q signal frequency components are an example of second signalfrequency components and represent components of each frequency of theanalog Q signal to be outputted.

[0081] The skew frequency component calculating unit 326, aconfiguration of which is the same as the skew frequency componentcalculating unit 126 regarding FIG. 1, calculates skew frequencycomponents representing phase errors of each frequency of the analog Qsignal corresponding to the analog I signal, on the basis of the skew oftiming with which a corrected digital I signal and a corrected digital Qsignal outputted by the correcting process unit 320 are corrected by theDA converter 380. Here, the corrected digital I signal and the correcteddigital Q signal are an example of a first digital signal and a seconddigital signal. More particularly, the skew frequency componentcalculating unit 326 may calculate a correcting function in thefrequency domain correcting the skew with the skew frequency components.

[0082] The second signal frequency component correcting unit 330, aconfiguration of which is the same as the second signal frequencycorrecting unit 130 regarding FIG. 1, corrects Q signal frequencycomponents, which the second digital signal calculating unit 334 uses togenerate a corrected digital Q signal, on the basis of the skewfrequency components calculated by the skew frequency componentcalculating unit 326. More particularly, the second signal frequencycomponent correcting unit 330 may correct the Q signal frequencycomponents by multiplying the Q signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 326. And, the second signalfrequency component correcting unit 330 may correct the Q signalfrequency components on the basis of the skew frequency components andthe I signal frequency components.

[0083] The first signal frequency component correcting unit 328, aconfiguration of which is the same as the first signal frequencycorrecting unit 128 regarding FIG. 1, corrects I signal frequencycomponents, which the first digital signal calculating unit 332 uses togenerate a corrected digital I signal, on the basis of the skewfrequency components calculated by the skew frequency componentcalculating unit 326. More particularly, the first signal frequencycomponent correcting unit 328 may correct the I signal frequencycomponents by multiplying the I signal frequency components by thecorrecting function in the frequency domain calculated by the skewfrequency component calculating unit 326. And, the first signalfrequency component correcting unit 328 may correct the I signalfrequency components on the basis of the skew frequency components andthe Q signal frequency components. Here, in case the second signalfrequency component correcting unit 330 completely corrects the skewcomponents with respect to Q frequency components, the first signalfrequency component correcting unit 328 may, without changing the Isignal frequency components, output to the first digital signalscalculating unit 332.

[0084] The first digital signal calculating unit 332, a configuration ofwhich is the same as the corrected first signal calculating unit 140regarding FIG. 1, generating a corrected digital I signal on the basisof the I signal frequency components. More particularly, the firstdigital signal calculating unit 332 converts the I signal frequencycomponents, spectrums of the digital I input signal in the frequencydomain corrected by the first signal frequency component correcting unit328, into the corrected digital I signal in the time domain by, forexample, performing the inverse discrete Fourier-transform. The seconddigital signal calculating unit 334, a configuration of which is thesame as the corrected second signal calculating unit 142 regarding FIG.1, generating a corrected digital Q signal on which the skew iscorrected like the first digital signal calculating unit 332. Themultiplexer 338 and the multiplexer 340, in case the skew measuring unit323 measures the skew, inputs the same reference signal to the DAconverter 380. Meanwhile, in case the waveform generating apparatus 300outputs the analog I signal and the analog Q signal corresponding to thedigital I input signal and the digital Q input signal, the correcteddigital I signal and the digital Q signal corrected by the first digitalsignal calculating unit 332 and the second the digital signalcalculating unit 334 are inputted to DA converter 380.

[0085] The DA converter 380 converts the corrected digital I signal andthe digital Q signal into the analog I signal and the analog Q signalwith a predetermined converting time interval respectively. The DAconverter 380 includes a reference clock generator 382, a first DAconverter 384 and a second DA converter 386.

[0086] The reference clock generator 382 generates a converting clocksignal representing timing with which a pair of corrected digitalsignals inputted by the correcting process unit 320 are converted by thefirst DA converter 384 and the second DA converter 386. The first DAconverter 384 converts the corrected digital I signal into the analog Isignal on the basis of the converting clock signal. The second DAconverter 386 converts the corrected digital Q signal into the analog Qsignal on the basis of the converting clock signal.

[0087] In this regard, description of a method for correcting the skewregarding the first signal frequency component calculating unit 324, thesecond signal frequency component calculating unit 325, the skewfrequency component calculating unit 326, the first signal frequencycomponent correcting unit 328 and the second signal frequency componentcorrecting unit 330 will be omitted, since the method is same asdescribed with regard to FIG. 1 using equations(1) to (18-2).

[0088] In addition, the correcting process unit 320 may not include thefirst signal frequency component calculating unit 324 and the secondsignal frequency component calculating unit 325. In this case, thecorrecting process unit 320 may generate the corrected digital I signaland the corrected digital Q signal on the basis of the I signalfrequency component and the Q signal frequency component inputted by thefirst signal frequency component correcting unit 328 and the secondsignal frequency component correcting unit 330, and output to the DAconverter 380.

[0089]FIG. 4 shows a process flow of a waveform generating apparatus 300relating to the second exemplary embodiment of the present invention.First, In order to measure the skew of converting timing of the first DAconverter 384 and the second DA converter 386, the reference signalgenerator 322 inputs the same reference signal to the first DA converter384 and the second DA converter 386 via the multiplexer 338 and themultiplexer 340(S400). The first DA converter 384 and the second DAconverter 386 convert the reference signal inputted into the analog Isignal and the analog Q signal respectively (S410). The skew measuringunit 323 measures the skew on the basis of an amount of a phasedifference between the analog I signal and the analog Q signal (S420).And the skew frequency component calculating unit 326 calculates theskew frequency components representing phase errors of each frequency ofthe analog Q signal corresponding to the analog I signal on the basis ofthe skew measured by the skew measuring unit 323(S430).

[0090] Next, the first signal frequency component calculating unit 324and the second signal frequency component calculating unit 325 input thedigital I input signal and the digital Q input signal to be convertedinto the analog signals synchronized respectively(S440). And, the firstsignal frequency component calculating unit 324 and the second signalfrequency component calculating unit 325 calculate the I signalfrequency components and the Q signal frequency components respectivelyon the basis of the digital I input signal and the digital Q inputsignal(S450). Next, the first signal frequency component correcting unit328 and the second signal frequency component correcting unit 330correct the I signal frequency components and the Q signal frequencycomponents on the basis of the skew frequency components calculated bythe skew frequency component calculating unit 326(S460). Next, the firstdigital signals calculating unit 332 and the second digital signalscalculating unit 334 calculate the corrected digital I signal and thecorrected digital Q signal on which the skew is corrected on the basisof the corrected I signal frequency components and the Q signalfrequency components respectively (S470). And, the first DA converter384 and the second DA converter 386 convert the corrected digital Isignal and the corrected digital Q signal on which the skew is correctedinto the analog I signal and the analog Q signal respectively (S480).

[0091] According to the digitizer apparatus 100 described above, theskew of the sampling timing with which a pair of digital signals aresampled by the AD converter 380 can be corrected for digital signals infrequency domain corresponding to analog signals. In addition, amagnitude of the skew during operation is measured by the referencesignal generator 102 and the skew measuring unit 132 and the amount ofthe correction can be adjusted using the magnitude of the skew measuredso that the digitizer apparatus 100 with high precision can be achieved.

[0092]FIG. 5 shows a configuration of a digitizer apparatus 500 relatingto the third exemplary embodiment of the present invention. Thedigitizer apparatus 500 converts a pair of synchronous analog signals tobe observed into a pair of digital signals with equal sample timing.With regard to the conversion, the digitizer apparatus 500 prevents animpairment of quality of signal during digitizing a pair of analogsignals by correcting an error of sample timing with which a pair ofanalog signals are converted into digital signals respectively with adigital filter. The digitizer apparatus 500 includes an analog inputunit 101, an AD converter 110 and a correcting process unit 520.Description about the analog input unit 101 and the AD converter 110with regard to FIG. 5 will be omitted, since a configuration thereof isthe same as the analog input unit 101 and the AD converter 110 shown inFIG. 1.

[0093] The correcting process unit 520 corrects an error of convertingtiming and converts to a pair of digital signals with equal convertingtiming, while performing a predetermined filtering process on the pairof digital signals outputted by the AD converter 110. The correctingprocess unit 520 includes a first digital filter 522, a correctingfilter coefficient generator 526, a second digital filter 524 and a skewmeasuring unit 532.

[0094] The first digital filter 522 converts a digital I signal inputtedby the AD converter 110, an example of a first digital signal, on thebasis of a predetermined filter coefficient and generates a converteddigital I signal, an example of a first converted signal. Here, thefirst digital filter 522 may have a filter coefficient with whichperforming the filtering process such as a band-rejection filtering anda band-pass filtering on the digital I signal.

[0095] The correcting filter coefficient generator 526 generates acorrecting filter coefficient correcting the skew of the first ADconverter 114 and the second AD converter 116, besides a waveform of animpulse response of the correcting filter coefficient is same as thefirst digital filter 522, on the basis of the skew of timing with whicha pair of analog signals inputted to the analog input unit 101 aresampled by the AD converter 110 and the filter coefficient set in thefirst digital filter 522.

[0096] The second digital filter 524 converts a digital Q signalinputted by the AD converter 110, an example of a second digital signal,on the basis of a correcting filter coefficient generated by thecorrecting filter coefficient generator 526 and generates a converteddigital Q signal, an example of a second converted signal.

[0097] The skew measuring unit 532 measures the skew of timing withwhich a pair of analog signals inputted to the analog input unit 101 aresampled by the AD converter 110 and provides the skew to the correctingfilter coefficient generator 526. The skew measuring unit 532 accordingto this exemplary embodiment, in case the same reference signalgenerated by the reference signal generator 102 with a pair of analogsignals is inputted to the AD converter 110, measures the skew on thebasis of an amount of a phase difference between the digital I signaland the digital Q signal outputted by the first AD converter 114 and thesecond AD converter 116.

[0098] Next, an exemplary method for correcting the skew regarding thedigitizer apparatus 500 is described.

[0099] Here, it is assumed that the first digital filter 522 and thesecond digital filter 524 are FIR filter, where function h(t) denotesthe filter coefficient. In this case, the impulse response of the firstdigital filter 522, letting T be a sampling interval of the AD converter110 is represented as the following equation(19): $\begin{matrix}{{{h(t)}{\sum\limits_{k = 0}^{N - 1}\quad {\delta \left( {t - {kT}} \right)}}} = {\sum\limits_{k = 0}^{N - 1}\quad {{h({kT})}{{\delta \left( {t - {kT}} \right)}.}}}} & (19)\end{matrix}$

[0100] Here, the filter coefficient of the first digital filter 522 ish(k·T)(k=0, 1, . . . , N−1).

[0101] The correcting filter coefficient generator 526 generates thecorrecting filter coefficient correcting the skew τ, besides a waveformof the impulse response of the correcting filter coefficient is same asthe first digital filter 522, on the basis of the filter coefficient ofthe a first digital filter 522 and the skew τ. The impulse response ofthe second digital filter 524 by the correcting filter coefficient isrepresented as the following equation(20): $\begin{matrix}{{{h(t)}{\sum\limits_{k = 0}^{N - 1}\quad {\delta \left( {t - {kT} - \tau} \right)}}} = {\sum\limits_{k = 0}^{N - 1}\quad {{h\left( {{kT} - \tau} \right)}{{\delta \left( {t - {kT} - \tau} \right)}.}}}} & (20)\end{matrix}$

[0102] According to the correcting filter coefficient h(k·T−τ) shown inequation(20), the second digital filter 524 can correct the digital Qsignal delayed by the skew τ relative to the digital I signal to outputwith the same sampling timing as the digital I signal.

[0103] In addition, with regard to analog input unit 101 and the ADconverter 110, an error in amplitude and/or direct current components ofoutput value of the digital I signal against the digital Q signal andthe digital Q input signal against the analog I input signal may arise.That is, with regard to equation(20), an impulse function δ′(t−kT−τ),where the error in amplitude and direct current components arise, isrepresented as the following equation(21):

δ′(t−kT−τ)=αδ(t−kT−τ)+β  (21).

[0104] From equations(20) and (21), a filter function of the seconddigital filter 524 correcting the error in amplitude and direct currentcomponents is represented as the following equation(22): $\begin{matrix}{{\sum\limits_{k = 0}^{N - 1}\quad {{h\left( {{kT} - \tau} \right)}\frac{1}{\alpha}\left\{ {{\delta^{\prime}\left( {t - {kT} - \tau} \right)} - \beta} \right\}}} = {{\sum\limits_{k = 0}^{N - 1}\quad {\frac{1}{\alpha}{h\left( {{kT} - \tau} \right)}{\delta^{\prime}\left( {t - {kT} - \tau} \right)}}} + {\sum\limits_{k = 0}^{N - 1}\quad {\left( {- \frac{\beta}{\alpha}} \right){h\left( {{kT} - \tau} \right)}}}}} & (22)\end{matrix}$

[0105] In order to correct the phase errors, the error in amplitude andthe error in direct current components with equation (22), the digitizerapparatus 500 may be configured as following. The skew measuring unit532 operates as an error measuring unit measuring the error in amplitudeα and the error in direct current components β as well as the phaseerror τ. The correcting filter coefficient generator 526 generates1/·h(kT−τ) in equation(22) as the correcting filter coefficient, whilegenerating integer components, the second term in equation(22), as apart of the correcting filter coefficient. The second digital filter 524converts the digital Q signal using equation (22) on the basis of thecorrecting filter coefficient generated by the correcting filtercoefficient generator 526 and generates the converted digital Q signal.

[0106] Here, with regard to the skew measuring unit 532 operating as theerror measuring unit, a difference between the output values of thedigital I signal and the digital Q signal, in case the reference signalthat is zero in analog value inputted to the AD converter 110, may bethe error in direct current components β. And, a ratio of an average foramplitude of the digital I signal and the digital Q signal, in case morethan a kind of the reference signal inputted to the AD converter 110,may be the error in amplitude α.

[0107]FIG. 6 shows a process flow of a digitizer apparatus 500 relatingto the third exemplary embodiment of the present invention.

[0108] First, in order to measure the skew of the sample timing of thefirst AD converter 114 and the second AD converter 116, the referencesignal generator 102 inputs the reference signal to the first ADconverter 114 via the multiplexer 104 and the first analog unit 106 andinputs the same reference signal to the second AD converter 116 via themultiplexer 105 and the second analog unit 108(S600). The first ADconverter 114 and the second AD converter 116 convert the referencesignal inputted into the digital I signal and the digital Q signalrespectively (S610). The skew measuring unit 532 measures the skew onthe basis of an amount of the phase difference between the digital Isignal and the digital Q signal (S620).

[0109] Next, the correcting filter coefficient generator 526 generatesthe correcting filter coefficient correcting the skew, besides thewaveform of the impulse response of the correcting filter coefficient issame as the first digital filter 522, on the basis of the skew measuredby the skew measuring unit 132 and the filter coefficient set in thefirst digital filter 522(S630).

[0110] Next, the AD converter 110 inputs the analog I signal via themultiplexer 104 and the first analog unit 106, while inputting theanalog Q signal via the multiplexer 105 and the second analog unit108(S640). And, the first AD converter 114 and the second AD converter116 in the AD converter 110 sample a pair of analog signals inputted andconvert to the digital I signal and the digital Q signal respectively(S650).

[0111] Next, the first digital filter 522 converts the digital I signalinputted by the first AD converter 114 on the basis of the predeterminedthe filter coefficient and generates the converted digital I signal.And, the first digital filter 522 converts the digital Q signal inputtedby the AD converter 110 on the basis of the correcting filtercoefficient generated by the correcting filter coefficient generator 526and generates the converted digital Q signal (S660).

[0112] According to the digitizer apparatus 500 described above, theskew of sampling with which a pair of analog signals are sampled by theAD converter 110 can be corrected by changing at least one of a pair ofthe filter coefficients used for filtering a pair of digital signalssampled. And, a magnitude of the skew during operation is measured bythe reference signal generator 102 and the skew measuring unit 532 andthe correcting filter coefficient can be adjusted using the magnitude ofthe skew measured so that the digitizer apparatus 500 with highprecision can be achieved.

[0113]FIG. 7 shows a configuration of a waveform generating apparatus700 relating to the fourth exemplary embodiment of the presentinvention. The waveform generating apparatus 700 inputs a pair ofdigital input signals to be converted into analog signals, which shouldbe synchronized, and converts and outputs a pair of analog signalssynchronized. With regard to this conversion, the waveform generatingapparatus 700 prevents the impairment of quality of signal duringconverting a pair of digital input signal into analog signals bycorrecting an error of converting timing with which a pair of digitalinput signal are converted into the analog signals respectively by adigital filter. The waveform generating apparatus 700 includes acorrecting process unit 720 and a DA converter 380. Description aboutthe DA converter 380 regarding FIG. 7 is omitted, since the DA converter380 has the same configuration as the DA converter 380 shown in FIG. 3.

[0114] The correcting process unit 720 inputs a digital I input signaland a digital Q input signal in quadrature each other, an example of apair of digital input signals to be converted into the analog signalssynchronized. The correcting process unit 720 includes a referencesignal generator 722, a skew measuring unit 723, a first digital filter726, a correcting filter coefficient generator 724, a second digitalfilter 728, a multiplexer 730 and a multiplexer 732.

[0115] The reference signal generator 722, which has the sameconfiguration as the reference signal generator 322, generates areference signal, which the skew measuring unit 723 uses to measure askew of timing with which a pair of digital input signals are convertedby the DA converter 380. The skew measuring unit 723, which has the sameconfiguration as the reference signal generator 323, measures the skewof timing with which a pair of digital signal outputted by thecorrecting process unit 720 to the DA converter 380 are converted by theDA converter 380, and provides the skew to the correcting filtercoefficient generator 724. The skew measuring unit 723 according to thisexemplary embodiment, in case the same reference signal generated by thereference signal generator 722 is inputted to the DA converter 380,measure the skew on the basis of an amount of a phase difference betweena analog I signal and a analog Q signal outputted by the first DAconverter 384 and the second DA converter 386 in the DA converter 380,an example of the first analog signal and the second analog signal.

[0116] The first digital filter 726, which has the same configuration asthe first digital filter 522 regarding FIG. 5, converts the digital Iinput signal representing a signal value of the analog I signal to beoutputted by the waveform generating apparatus 700 on the basis of apredetermined first filter coefficient, and generates a converteddigital I signal, an example of a first converted signal.

[0117] The correcting filter coefficient generator 724, which has thesame configuration as the correcting filter coefficient generator 526regarding FIG. 5, generates a second filter coefficient correcting theskew, besides a waveform of the impulse response of the second filtercoefficient is same as the first digital filter 522, on the basis of theskew of timing with which the analog I signal and the analog Q signalare converted by the DA converter 380 and a first filter coefficient,and sets in the second digital filter 728.

[0118] The second digital filter 728, which has the same configurationas the second digital filter 524 regarding FIG. 5, converts the digitalQ input signal representing a signal value of the analog Q signal to beoutputted by the waveform generating apparatus 700 on the basis of asecond filter coefficient, and generates a converted digital Q signal,an example of a second converted signal.

[0119] The multiplexer 730 and the multiplexer 732 input the samereference signal to the DA converter 380, in case the skew measuringunit 723 measures the skew. Meanwhile, in case the waveform generatingapparatus 700 outputs an analog I signal and an analog Q signalcorresponding to the digital I input signal and the digital Q inputsignal via the DA converter 380, the converted digital I signal and theconverted digital Q signal are inputted to the DA converter 380.

[0120]FIG. 8 shows a process flow of a waveform generating apparatus 700relating to the fourth exemplary embodiment of the present invention.

[0121] First, in order to measure the skew of converting timing of thefirst DA converter 384 and the second DA converter 386, the referencesignal generator 722 inputs the same reference signal to the first DAconverter 384 and the second DA converter 386 via the multiplexer 730and the multiplexer 732(S800). The first DA converter 384 and the secondDA converter 386 convert the reference signal inputted into the analog Isignal and the analog Q signal respectively (S810). The skew measuringunit 723 measures the skew on the basis of an amount of the phasedifference between the analog I signal and the analog Q signal (S820).And, the correcting filter coefficient generator 724 generates thesecond filter coefficient correcting the skew, besides the waveform ofthe impulse response of the second filter coefficient is same as thefirst digital filter 522, on the basis of the skew measured by the skewmeasuring unit 723 and the first filter coefficient, and sets in thesecond digital filter 728(S830).

[0122] Next, the first digital filter 726 and the second digital filter728 input the digital I input signal and the digital Q input signalrespectively, which should be converted into the analog signalssynchronized (S840). The first digital filter 726 converts the digital Iinput signal on the basis of the first filter coefficient, and generatesthe converted digital I signal. The second digital filter 728 convertsthe digital Q input signal on the basis of the second filter coefficientgenerated by the correcting filter coefficient generator 724, andgenerates the converted digital Q signal (S850). The first DA converter384 and the second DA converter 386 convert the converted digital Isignal and the converted digital Q signal on which the skew is correctedinto the analog I signal and the analog Q signal respectively (S860).

[0123] In this regard, description of a method for correcting the skewregarding the correcting filter coefficient generator 724, the firstdigital filter 726 and the second digital filter 728 will be omitted,since the method is same as described with regard to FIG. 6 usingequations (19) and (20).

[0124] According to the digitizer apparatus 700 described above, theskew of sampling with which the DA converter 380 converts to a pair ofsynchronous analog signals can be corrected by digital filtering digitalsignals corresponding to the analog signals to be outputted in thefrequency domain. And, a magnitude of the skew during operation ismeasured by the reference signal generator 722 and the skew measuringunit 723 and an amount of the correction can be adjusted using themagnitude of the skew measured so that the digitizer apparatus 700 withhigh precision can be achieved.

[0125]FIG. 9 shows an exemplary hardware configuration of a digitizerapparatus 100, a waveform generating apparatus 300, a digitizerapparatus 500 and/or a waveform generating apparatus 700 relating to anexemplary embodiment of the present invention. The digitizer apparatus100, the waveform generating apparatus 300, the digitizer apparatus 500and/or the waveform generating apparatus 700, according to thisexemplary embodiment of the present invention, include a CPU 900, a ROM910, a RAM 920, a communication interface 930, a hard disc driver 940, aflexible disc driver 950 and a CD-ROM driver 960, and are implemented bythe information processing apparatus 890 coupled to the AD converter 110and/or the DA converter 380 via the analog input unit 101

[0126] The CPU 900 operates on the basis of programs installed in theROM 910 and the RAM 920, and controls each parts. The ROM 910 contains aboot program executed by the CPU 900 when the information processingapparatus 890 drives or programs depending on hardware of theinformation processing apparatus 890. The RAM 920 contains programsexecuted by the CPU 900 and data used by the CPU 900. The communicationinterface 930 communicates other apparatuses via communication networks.The hard disc driver 940 contains programs and data used by theinformation processing apparatus 890 and provides the programs and datato the CPU 900 via RAM 920. The flexible disc driver 950 reads programsor data from a flexible disc 990 and provides the programs or data tothe RAM 920. The CD-ROM driver 960 reads programs or data from a CD-ROM995 and provides the programs or data to the RAM 920.

[0127] Programs provided to the CPU 900 via the RAM 920 are contained ina recording medium such as the flexible disc 990, the CD-ROM 995 or a ICcard and provided to a user. The programs are read from the recordingmedium, installed in the information processing apparatus 890 via theRAM 920 and executed for the information processing apparatus 890.

[0128] A program, which is installed in the information processingapparatus 890, executed and allows the information processing apparatus890 to function as the digitizer apparatus 100, includes a first signalfrequency component calculating module, a second signal frequencycomponent calculating module, a skew frequency component calculatingmodule, a first signal frequency correcting module, a second signalfrequency correcting module, a skew measuring module, a corrected firstsignal calculating module and a corrected second signal calculatingmodule. These program or modules allow the information processingapparatus 890 to function as a first signal frequency componentcalculating unit 122, a second signal frequency component calculatingunit 124, a skew frequency component calculating unit 126, a firstsignal frequency correcting unit 128, a second signal frequencycorrecting unit 130, a skew measuring unit 132, a corrected first signalcalculating unit 140 and a corrected second signal calculating unit 142respectively.

[0129] A program, which is installed in the information processingapparatus 890, executed and allows the information processing apparatus890 to function as the waveform generating apparatus 300, includes areference signal generating module, a skew measuring module, a firstsignal frequency component calculating module, a second signal frequencycomponent calculating module, a skew frequency component calculatingmodule, a first signal frequency component correcting module, a secondsignal frequency component correcting module, a first digital signalcalculate module and a second digital signal calculate module. Theseprogram or modules allow the information processing apparatus 890 tofunction as a reference signal generator 322, a skew measuring unit 323,a first signal frequency component calculating unit 324, a second signalfrequency component calculating unit 325, a skew frequency componentcalculating unit 326, a first signal frequency component correcting unit328, a second signal frequency component correcting unit 330, a firstdigital signal calculating unit 332 and a second digital signalcalculating unit 334 respectively.

[0130] A program, which is installed in the information processingapparatus 890, executed and allows the information processing apparatus890 to function as the digitizer apparatus 500, includes a first digitalfilter module, a second digital filter module, a correcting filtercoefficient generating module and a skew measuring module. These programor modules allows the information processing apparatus 890 to functionas a first digital filter 522, a second digital filter 524, a correctingfilter coefficient generator 526 and a skew measuring unit 532respectively.

[0131] A program, which is installed in the information processingapparatus 890, executed and allows the information processing apparatus890 to function as the waveform generating apparatus 700, includes areference signal generating module, a skew measuring module, acorrecting filter coefficient generating module, a first digital filtermodule and second digital filter module. These program or modules allowsthe information processing apparatus 890 to function as a referencesignal generator 722, a skew measuring unit 723, a correcting filtercoefficient generator 724, a first digital filter 726 and a seconddigital filter 728.

[0132] The programs and modules described above may be contained anexternal recording medium. As the recording medium, an optical recordingmedium such as a DVD or a PD as well as the flexible disc 990 and theCD-ROM 995, an optical magnetic recording medium such as MD, a tapemedium and semiconductor memory such as the IC card can be used. And,the programs may be provided from an external network to the informationprocessing apparatus 890 via the communication network by using memorydevices such as a hard disc or a RAM installed in a server systemconnected to a leased communication network or internet as the recordingmedium.

[0133] Although the present invention has been described by way ofexemplary embodiments, it should be understood that those skilled in theart might make many changes and substitutions without departing from thespirit and the scope of the present invention, which is defined by theappended claims.

[0134] For example, a pair of analog input signals inputted by thedigitizer apparatus 100 or the digitizer apparatus 500 or a pair ofanalog signals generated by the waveform generating apparatus 300 or thewaveform generating apparatus 700 are not limited to quadrature signalsand may be any kinds of synchronous analog signals.

[0135] It is apparent from the description above that, according to thepresent invention, a difference of sample timing or converting timingbetween a pair of signals to be synchronized is suppressed so that adigitizer module, a waveform generating module, a converting method anda waveform generating method, preventing an impairment of quality ofsignal, and a recording medium for recording a program thereof can beachieved.

What is claimed is:
 1. A digitizer module for converting a pair ofanalog signals into a pair of digital signals with equal sample timing,comprising: an AD converter for sampling said pair of analog signals ata predetermined time interval and converting into a first and seconddigital signals respectively; a second signal frequency componentcalculating unit for calculating a second signal frequency componentrepresenting a component of each frequency of said second digital signalon the basis of said second digital signal; a skew frequency componentcalculating unit for calculating a skew frequency component representinga phase error of each frequency of said second digital signalcorresponding to said first digital signal on the basis of a skew of atiming with which said pair of analog signals are sampled by said ADconverter; and a second signal frequency component correcting unit forcorrecting said second signal frequency component on the basis of saidskew frequency component.
 2. A digitizer module as claimed in claim 1further comprising a corrected second signal calculating unit forcalculating said second digital signal on which said skew has beencorrected on the basis of said second signal frequency component, whichis corrected.
 3. A digitizer module as claimed in claim 1, wherein saidsecond signal frequency component calculating unit calculates saidsecond signal frequency component by performing a discreteFourier-transform on said second digital signal, said skew frequencycomponent calculating unit calculates a correcting function in afrequency domain for correcting said skew with said skew frequencycomponent, and said second signal frequency component correcting unitcorrects said second signal frequency component by multiplying saidsecond signal frequency component by said correcting function in saidfrequency domain.
 4. A digitizer module as claimed in claim 1 furthercomprising a first signal frequency component calculating unit forcalculating a first signal frequency component representing a componentof each frequency of said first digital signal on the basis of saidfirst digital signal, wherein said second signal frequency componentcorrecting unit corrects said second signal frequency component on thebasis of said skew frequency component and said first signal frequencycomponent.
 5. A digitizer module as claimed in claim 1 furthercomprising a second signal frequency component calculating unit forcalculating a first signal frequency component representing a componentof each frequency of said first digital signal on the basis of saidfirst digital signal and a first signal frequency component correctingunit for correcting said first signal frequency component on the basisof said skew frequency component.
 6. A digitizer module as claimed inclaim 1 further comprising a skew measuring unit for measuring said skewon the basis of an amount of a phase difference between said first andsecond digital signals, in case a same signal as said pair of analogsignals is inputted to said AD converter.
 7. A digitizer module forconverting a pair of analog signals into a pair of digital signals withequal sample timing, comprising: an AD converter for sampling said pairof analog signals at a predetermined time interval and converting into afirst and a second digital signals; a first digital filter forgenerating a first converted signal into which said first digital signalis converted on the basis of a predetermined filter coefficient; acorrecting filter coefficient generator for generating a correctingfilter coefficient correcting a skew, besides a waveform of an impulseresponse of said correcting filter coefficient is same as said firstdigital filter, on the basis of said skew of a timing with which saidpair of analog signals are sampled by said AD converter and apredetermined filter coefficient; and a second digital filter forconverting said second digital signal on the basis of said correctingfilter coefficient and generating a second converted signal on whichsaid skew is corrected.
 8. A digitizer module as claimed in claim 7,wherein said correcting filter coefficient generator makes saidcorrecting filter coefficient be h(k·T□τ), in case said predeterminedfilter coefficient is h(k·T) and said skew is τ, where said firstdigital filter has at least two said predetermined filter coefficient, kdenotes an integer in a range of zero to a number one less than thenumber of said predetermined filter coefficient and T denotes a samplinginterval of said AD converter.
 9. A waveform generating module foroutputting a pair of synchronous analog signals, comprising: a firstdigital signal calculating unit for generating a first digital signal onthe basis of a first signal frequency component representing a componentof each frequency of a first analog signal, which said waveformgenerating module should output; a second digital signal calculatingunit for generating a second digital signal on the basis of a secondsignal frequency component representing a component of each frequency ofa second analog signal, which said waveform generating module shouldoutput; a DA converter for converting said first and second digitalsignals into said first and second analog signals at a predeterminedtime interval respectively; a skew frequency component calculating unitfor calculating a skew frequency component representing a phase error ofeach frequency of said second analog signal corresponding to said firstanalog signal, on the basis of a skew of a timing with which said firstand second digital signals are converted by said DA converter; and asecond signal frequency component correcting unit for correcting saidsecond signal frequency component used for generating said seconddigital signal by said second digital signal calculating unit on thebasis of said skew frequency component.
 10. A waveform generating moduleas claimed in claim 9, wherein said skew frequency component calculatingunit calculates a correcting function in a frequency domain forcorrecting said skew with said skew frequency component, said secondsignal frequency component correcting unit corrects said second signalfrequency component by multiplying said second signal frequencycomponent by said correcting function in said frequency domain and saidsecond digital signal calculating unit generates said second digitalsignal by performing an inverse discrete Fourier-transform on saidsecond signal frequency component corrected by said second signalfrequency component correcting unit.
 11. A waveform generating module asclaimed in claim 9, wherein said second signal frequency componentcorrecting unit corrects said second signal frequency component used forgenerating said second digital signal by said second digital signalscalculating unit, on the basis of said skew frequency component and saidfirst signal frequency component.
 12. A waveform generating module asclaimed in claim 9 further comprising a first signal frequency componentcorrecting unit for correcting said first signal frequency componentused for generating said first digital signal by said first digitalsignal calculating unit, on the basis of said skew frequency component.13. A waveform generating module as claimed in claim 9 furthercomprising a skew measuring unit for measuring said skew on the basis ofan amount of a phase difference between said first and second analogsignals, in case a same signal as said first and second digital signalsis inputted to said DA converter.
 14. A waveform generating module foroutputting a pair of synchronous analog signals, comprising: a firstdigital filter for generating a first converted signal into which afirst digital signal, which represents a signal value of a first analogsignal to be outputted, is converted on the basis of a first filtercoefficient; a second digital filter for generating a second convertedsignal into which a second digital signal, which represents a signalvalue of a second analog signal to be outputted, is converted on thebasis of a second filter coefficient; a DA converter for converting saidfirst and second digital signals into said first and second analogsignals at a predetermined time interval respectively; and a correctingfilter coefficient generator for generating said second filtercoefficient correcting a skew, besides a waveform of an impulse responseof said correcting filter coefficient is same as said first digitalfilter, on the basis of said skew of a timing with which said DAconverter converts said first and second digital signals into said firstand second analog signals and said first filter coefficient.
 15. Awaveform generating module as claimed in claim 14, wherein saidcorrecting filter coefficient generator makes said second filtercoefficient be h(k·T−i), in case said first filter coefficient is h(k·T)and said converting timing error is τ, where said first digital filterhas at least two said first filter coefficient, k denotes an integer ina range of zero to a number one less than the number of said firstfilter coefficient and T denotes a converting interval of said DAconverter.
 16. A recording medium for recording a program used for adigitizer module converting a pair of analog signals into a pair ofdigital signals with equal sample timing, wherein said digitizer modulecomprises an AD converter for sampling said pair of analog signals at apredetermined time interval and converting said pair of analog signalsinto a first and second digital signals, and said program allows saiddigitizer module to function with: a second signal frequency componentcalculating unit for calculating a second signal frequency componentrepresenting a component of each frequency of said second digital signalon the basis of said second digital signal; a skew frequency componentcalculating unit for calculating a skew frequency component representinga phase error of each frequency of said second digital signalcorresponding to said first digital signal, on the basis of said skew ofa timing with which said pair of analog signals are sampled by said ADconverter; and a second signal frequency component correcting unit forcorrecting said second signal frequency component on the basis of saidskew frequency component.
 17. A converting method for converting a pairof analog signals into a pair of digital signals with equal sampletiming, comprising the steps of: sampling said pair of analog signals ata predetermined time interval and converting said pair of analog signalsinto a first and second digital signals respectively; calculating asecond signal frequency component representing a component of eachfrequency of said second digital signal on the basis of said seconddigital signal; calculating a skew frequency component representing aphase error of each frequency of said second digital signalcorresponding to said first digital signal, on the basis of said skew ofa timing with which said pair of analog signals are sampled during saidstep of sampling and converting; and correcting said second signalfrequency component on the basis of said skew frequency component.
 18. Arecording medium for recording a program used for a digitizer moduleconverting a pair of analog signals into a pair of digital signals withequal sample timing, wherein said digitizer module comprises an ADconverter for sampling said pair of analog signals at a predeterminedtime interval and converting said pair of analog signals into a firstand second digital signals, and said program allows said digitizermodule to function with: a first digital filter for generating a firstconverted signal into which said first digital signal is converted onthe basis of a predetermined filter coefficient; a correcting filtercoefficient generator for generating a correcting filter coefficientcorrecting a skew, besides a waveform of an impulse response of saidcorrecting filter coefficient is same as said first digital filter, onthe basis of said skew of a timing with which said first and secondanalog signals are converted by said AD converter and said predeterminedfilter coefficient; and a second digital filter for converting saidsecond digital signal on the basis of said correcting filter coefficientand generating a second converted signal on which said skew iscorrected.
 19. A converting method for converting a pair of analogsignals into a pair of digital signals with equal sample timing,comprising the steps of: sampling said pair of analog signals at apredetermined time interval and converting said pair of analog signalsinto a first and second digital signals respectively; generating a firstconverted signal into which said first digital signal is converted onthe basis of a predetermined filter coefficient; generating a correctingfilter coefficient correcting a skew, besides a waveform of an impulseresponse of said correcting filter coefficient is same as said step ofgenerating said first converted signal, on the basis of said skew of atiming with which said first and second analog signals are converted bysaid AD converter and said predetermined filter coefficient; andconverting said second digital signal on the basis of said correctingfilter coefficient and generating a second converted signal on whichsaid skew is corrected.
 20. A recording medium for recording a programused for a waveform generating module outputting a pair of synchronousanalog signals, wherein said waveform generating module comprises a DAconverter for converting a first and second digital signals into a firstand second analog signals at a predetermined time interval respectively,and said program allows said waveform generating module to functionwith: a first digital signal calculating unit for generating said firstdigital signal on the basis of a first signal frequency componentrepresenting a component of each frequency of said first analog signal,which should be outputted by said waveform generating module; a seconddigital signal calculating unit for generating said second digitalsignal on the basis of a second signal frequency component representinga component of each frequency of said second analog signal, which shouldbe outputted by said waveform generating module; a skew frequencycomponent calculating unit for calculating a skew frequency componentrepresenting a phase error of each frequency of said second analogsignal corresponding to said first analog signal, on the basis of saidskew of a timing with which said first and second digital signals areconverted by said DA converter; and a second signal frequency componentcorrecting unit for correcting said second signal frequency componentused for generating said second digital signal by said second digitalsignal calculating unit, on the basis of said skew frequency component.21. A waveform generating method for outputting a pair of synchronousanalog signals, comprising the steps of: generating a first digitalsignal on the basis of a first signal frequency component representing acomponent of each frequency of a first analog signal, which should beoutputted; generating a second digital signal on the basis of a secondsignal frequency component representing a component of each frequency ofa second analog signal, which should be outputted; converting said firstand second digital signals into said first and second analog signals ata predetermined time interval respectively; calculating a skew frequencycomponent representing a phase error of each frequency of said secondanalog signal corresponding to said first analog signal, on the basis ofa skew of a timing with which said first and second digital signals areconverted during said step of converting; and correcting said secondsignal frequency component used for generating said second digitalsignal during said step of generating said second digital signal, on thebasis of said skew frequency component.
 22. A recording medium forrecording a program used for a waveform generating module outputting apair of synchronous analog signals, wherein said waveform generatingmodule comprises a DA converter for converting a first and seconddigital signals into a first and second analog signals at apredetermined time interval respectively, and said program allows saidwaveform generating module to function with: a first digital filter forgenerating a first converted signal into which a first digital signal,which represents a signal value of said first analog signal to beoutputted, is converted on the basis of a first filter coefficient; asecond digital filter for generating a second converted signal intowhich a second digital signal, which represents a signal value of saidsecond analog signal to be outputted, is converted on the basis of asecond filter coefficient; and a correcting filter coefficient generatorfor generating said second filter coefficient correcting a skew, besidesa waveform of an impulse response of said correcting filter coefficientis same as said first digital filter, on the basis of said skew of atiming with which said first and second digital signals converted intosaid first and second analog signals by said DA converter and said firstfilter coefficient.
 23. A waveform generating method for outputting apair of synchronous analog signals, comprising the steps of: generatinga first converted signal into which a first digital signal, whichrepresents a signal value of a first analog signal to be outputted, isconverted on the basis of a first filter coefficient; generating asecond converted signal into which a second digital signal, whichrepresents a signal value of a second analog signal to be outputted, isconverted on the basis of a second filter coefficient; converting saidfirst and second digital signals into said first and second analogsignals at a predetermined time interval respectively; and generatingsaid second filter coefficient correcting a skew, besides a waveform ofan impulse response of said second filter coefficient is same as saidfirst digital filter, on the basis of said skew of a timing with whichsaid first and second digital signals converted into said first andsecond analog signals during said step of converting and said firstfilter coefficient.